1. Field of the Disclosure
The present disclosure relates to an organic light emitting device, and more particularly, to an organic light emitting device, efficiency of which is improved by changing a layer structure, and a method for manufacturing the same.
2. Discussion of the Related Art
Image display devices, which display a variety of information on a screen, are being developed as a core technology of screen info-communication age. Such development is toward thinner, lighter, portable and higher-function trends. In this regard, as flat panel display devices capable of solving large weight and large volume, which are drawbacks of cathode-ray tubes (CRTs), organic light emitting displays that display images while controlling an amount of light emitted from an organic light emitting layer are attracting much attention.
Organic light emitting displays spontaneously emit light using a thin light emitting layer disposed between electrodes, thus advantageously enabling realization of a thin film like paper. Such an organic light emitting display is divided into an active matrix-type that can be selectively operated by cell drivers provided in respective pixels and a passive matrix-type that can be controlled according to respective lines.
Active matrix organic light emitting displays (AMOLED) display an image through pixels including three color (R, G, B) pixel groups arrayed in a matrix form. Each pixel includes an organic light emitting device such as an organic light emitting diode and a cell driver driving the organic light emitting diode. The cell driver includes a gate line to supply a scan signal, a data line to supply a video data signal, and at least two thin film transistors between common power lines to supply a common power signal and drive an anode of the organic light emitting diode.
The organic light emitting device includes an anode, a hole injection layer (HIL), a hole transport layer (HTL), a light emitting layer, an electron transport layer (ETL), an electron injection layer (EIL), and a cathode.
Such an organic light emitting device is generally known to be formed by separately vacuum-depositing (vacuum-evaporating) respective layers. In accordance with vacuum deposition, materials for layers to be formed are deposited in a gas state in a vacuum chamber on a substrate.
In this regard, when a vacuum chamber is used, the size of the vacuum chamber should be at least larger than that of the substrate upon which vacuum deposition is performed, and the vacuum chamber has a difficulty in securing a sufficient space of width and length enabling introduction of the substrate into the chamber, thus having a limitation of increase in size and, if possible, it is difficult to maintain the size-increased chamber under vacuum. For this reason, other methods for manufacturing organic light emitting devices have been considered.
For example, a method of forming layers in a solution state on a substrate through a solution process, without using a chamber requiring additional vacuum conditions is suggested.
However, a part of layers constituting the organic light emitting device have poor stability due to inherent characteristics of materials thereof, thus being disadvantageously unsuitable for the solution process. In particular, when a blue light emitting material is used for formation of light emitting layer through the solution process and is then applied to displays, sufficient characteristics cannot be obtained. Accordingly, in recent years, a method of separately forming a blue light emitting layer and a green light emitting layer has been suggested. Such a conventional organic light emitting device has the following disadvantages.
In recent years, a hybrid-type organic light emitting device having a structure in which a red light emitting layer and a green light emitting layers are separately formed in each pixel and a blue light emitting layers is formed throughout the pixels in common has been known.
However, since, in this structure, the blue light emitting layer is formed throughout the pixels, there are regions where the red light emitting layer overlaps the green light emitting layer and, in these regions, color purity is disadvantageously decreased due to color mixing of emitting light.
In order to increase the color purity, various structures have been suggested. However, these structures have a problem in that a driving voltage is increased, when color purity is improved. Hybrid organic light emitting devices having a structure capable of improving color purity, while reducing a driving voltage have not yet been developed.
Also, there is a demand for application of solution processes to hybrid devices, but layers unsuitable for solution processes due to inherent limitations of materials are present and, for this reason, there is a difficulty in stably applying a solution process to a plurality of layers due to damage to the surface of layers formed by a solution process when the solution process is used in conjunction with vacuum deposition.